The present invention relates to silencing equipment for electronic devices, and more particularly to silencing equipment for electronic devices, the equipment having a simple structure and being adapted to be installed to an electronic device capable of cooling a heat generating section thereof with air, in order to reduce the level of noise generated by a fan.
In recent years, electronic devices called blade servers have rapidly spread. A blade server includes multiple servers that are installed in a chassis and attachable to or removable from the chassis. Utilizing the blade server has significantly increased the server installation density in the chassis. With the increase in the server installation density, the number of fans that cool heat generating sections (CPU, memory, hard disk and the like) provided in the servers and the rotation speed of the fans have been increased. As a result, the level of noise generated by the electronic device has increased.
The chassis can be downsized due to the increase in the server installation density. Thus, a case in which a blade server is installed in an office has been increased. This makes a request strong for reducing the level of noise generated by a blade server. To satisfy such a request for reducing the level of noise, silencing equipment including an acoustic absorbent member made of glass wool or urethane is installed in the vicinity of a fan or in a chassis in many cases. Such silencing equipment provides a silencing effect on a frequency band on the basis of acoustic absorption characteristics of the acoustic absorbent member.
The following describes conventional silencing equipment for electronic devices with reference to FIG. 16.
FIG. 16 is a cross sectional view of the conventional silencing equipment for electronic devices.
JP-A-H05-226864 discloses a conventional silencing structure for an electronic device, the structure being the same as that of the equipment described above.
A typical electronic device such as a blade server includes a chassis 13, a fan 15 and a plurality of servers 16 having heat generating sections such as CPUs. Cooling air enters the electronic device through an intake port 14 and flows out of the electronic device through an exhaust port 20. A silencing structure 17 includes a plurality of acoustic absorbent members 18, 19, 21 and 22 which are located in the vicinity of the fan 15 or in the vicinity of the intake or exhaust port in order to reduce the level of noise generated by the fan 15.
A problem with the conventional silencing equipment for electronic devices is described below with reference to FIGS. 16 to 18.
FIG. 17 is a graph showing the relationship between a frequency of noise generated by the fan and the noise level.
FIG. 18 is a graph showing the relationship between a frequency of noise to be absorbed by a general acoustic absorbent material and a sound absorption rate.
The plurality of acoustic absorbent members 18, 19, 21 and 22 form the silencing structure 17 of the conventional silencing equipment for electronic devices as shown in FIG. 16, to reduce the level of noise generated by the fan 15. The noise generated by the fan 15 has a specified peak frequency that is relatively low in many cases. As shown in FIG. 18, however, a general acoustic absorbent member made of glass wool or urethane absorbs more noise with a high frequency compared with noise with a low frequency. It is, therefore, necessary that the acoustic absorbent members 18, 19, 21 and 22 have large thicknesses and large areas in order to significantly reduce the level of noise generated by the fan 15 shown in FIG. 16. There has been a problem that the size of the silencing structure 17 increases. In addition, as fluid resistance increases due to the increase in the size of the silencing structure, cooling air is prevented from passing through the silencing equipment. Furthermore, as the number of servers attachable to or removable from the electronic device such as a blade server changes, the amount of heat generated by the electronic device changes. Thus, it is necessary to change specifications of the electronic device, such as the rotation speed of the fan 15. As a result, frequency characteristics of the noise change. In this case, it is necessary to reconfigure the silencing structure 17 based on an allowable value of noise at the location at which the electronic device is installed.
The present invention is devised to solve the aforementioned problems. It is, therefore, an object of the present invention to provide silencing equipment for electronic devices that cool heat generating sections thereof with air, the silencing equipment having a small and simple structure and providing a large silencing effect to reduce the level of noise generated by a fan.